Principais experimentos em biologia molecular, Resumos de Biologia molecular

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molecularmolecular

biology biology

Robert Brown

Historic

Aim

Observe and describe structures present in plant cells. Brown examines plant cells from different parts of plants using a microscope he noticed a distinct central structure in each cell.

Results

Brown described the central structure as a "core" but he did not yet have a complete understanding of its function.

Conclusion

The discovery of the nucleus in plant cells was a significant advance in understanding cellular organization. Matthias Schleiden and Theodor Schwann 1838-

Aim

Establish the foundations of Cell Theory, which postulates that the cell is the basic unit of life.

Experiment

Scientists have carried out detailed observations of plant and animal tissues under the microscope They compared cellular structures in different tissue types.

Cell Theory

In 1839, Schleiden and Schwann combined their conclusions to formulate the Cell Theory. The cell is the basic unit of all living beings.

Conclusion

Schleiden concluded that all plants are composed of cells and that the cell is the basic unit of plant structure. Schwann concluded that all animals are composed of cells and that the cell is the basic unit of animal structure.

Experiment

Albrecht Kossel

Historic

Contributions

He studied the chemical composition of cells and focused on the analysis of nucleoproteins, which are complexes of proteins and nucleic acids. He isolated nucleic acids and demonstrated that they contained different types of nitrogenous bases.

Key Findings and

Contributions:

Kossel identified the nitrogenous bases adenine, cytosine, guanine and thymine in DNA, as well as uracil in RNA. He determined that these bases were fundamental components of nucleic acids. Kossel developed methods for analyzing the chemical composition of nucleic acids, demonstrating that they consisted of repeating units of nucleotides.

Nobel Prize:

Albrecht Kossel was awarded the Nobel Prize in Medicine or Physiology for his contributions to the understanding of the chemistry of nucleic acids and proteins. August Weismann 1887

Aim

Investigate whether changes acquired during the life of an organism could be transmitted to its descendants

Experiment

He carried out rat tail docking experiments over several generations. He observed that even after several generations of mice with docked tails, subsequent generations still had normal tails, disproving the idea that acquired changes affect inheritance.

Germinal Continuity

Theory

Only germ cells carry genetic information that is passed on to subsequent generations, while somatic cells do not affect heredity.

Conclusion

Germ cells (which give rise to eggs and sperm) are isolated from somatic cells (of the body) and therefore changes in the body do not affect the hereditary information in the germ cells.

Richard Altmann Historic

Aim

He investigated the chemical composition of "nuclein", a substance isolated from cell nuclei, and sought to understand its nature and components. isolated "nuclein" from cell nuclei using extraction techniques. He performed detailed chemical analyzes to determine the composition of "nuclein" and identify its fundamental components.

Results

identified that "nuclein" was composed of two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). observed that "nuclein" had an acidic nature, indicating the presence of acidic groups in its structure.

Conclusion

Altmann's discoveries about nucleic acids and the acidic nature of "nuclein" had a profound impact on molecular and cellular biology. Hugo de Vries, Carl Correns and Erich von Tschermak 1900

Context

Gregor Mendel's works on heredity were published in 1866, but his discoveries did not receive much attention until the end of the 19th century.

Rediscovery of Mendel's Laws

De Vries, Correns and Tschermak, independently of each other, rediscovered Mendel's laws in their own research. They carried out experiments with plants, mainly peas, to investigate the transmission of traits between generations.

Results

All three scientists observed consistent patterns of segregation and inheritance of traits in their plants, confirming Mendel's laws. They noticed that traits were transmitted according to predictable ratios, such as 3:1 for a dominant and recessive trait.

Conclusion

His observations reinforced the understanding that hereditary traits followed specific, quantifiable patterns.

Experiment

Historic

Aim

determine which chemical component of bacteria was responsible for the transfer of genetic characteristics, as observed in Frederick Griffith's experiment. Avery worked with the bacterium Streptococcus pneumoniae, focusing on the transfer of the polysaccharide capsule that determined virulence. carried out a series of enzymatic digestion experiments, separating different chemical components of bacteria.

Results

By degrading proteins and RNA, the virulence of the bacteria was not affected. However, by degrading DNA, the bacteria's ability to transfer virulence was lost.

Conclusion

Based on the results, Avery concluded that DNA was the component responsible for transmitting genetic characteristics. Rosalind Franklin 1948

Aim

investigate the molecular structure of DNA using the X-ray diffraction technique.

Experiment

Franklin worked with highly condensed and organized DNA fibers, rather than crystalline samples, to obtain more detailed information about the structure of DNA. She directed X-rays at DNA fibers and observed the resulting diffraction patterns, which revealed information about the molecule's internal structure.

Results

X-ray diffraction images of DNA fibers showed a characteristic speckled pattern, indicating the presence of a helical structure.

Conclusion

Results from X-ray diffraction of DNA fibers have provided important clues about the molecule's coiled-coil structure.

Experiment

Oswald Avery They treated the bacteria with specific enzymes to degrade proteins, RNA and DNA separately. His data influenced subsequent work by other scientists, such as James Watson and Francis Crick.

Historic

Aim

understand the composition of nitrogenous bases in nucleic acids and whether there was any regularity in the proportions between them. performed detailed analyzes of the composition of nitrogenous bases in different nucleic acids, including the DNA of several species. observed that the amount of adenine (A) in DNA molecules was approximately equal to the amount of thymine (T).

Results

formulated the famous "base pairing rules". These rules state that in DNA, A pairs with T and G pairs with C.

Conclusion

Chargaff's work on the proportions of nitrogenous bases in DNA molecules helped to consolidate the foundations of molecular genetics and DNA structure. Martha Chase e Alfred Hershey 1952

Aim

determine whether DNA or proteins were responsible for carrying genetic information in viruses.

Experiment

They used the T bacteriophage, a virus that infects Escherichia coli (E. coli) bacteria. To distinguish between the virus's DNA and proteins, Chase and Hershey labeled the DNA with radioactive phosphorus (32P) and the proteins with radioactive sulfur (35S).

Results

When only the DNA was labeled with 32P, infection of the bacteria resulted in the transfer of radioactive genetic material to the bacteria.

Conclusion

The DNA of the virus was the molecule that contained the genetic information necessary for the infection of bacteria.

Analytics

Erwin Chargaff Likewise, the amount of guanine (G) was approximately equal to the amount of cytosine (C) in the analyzed DNAs. The scientists infected E. coli bacteria with the tagged viruses, allowing the viruses to replicate in the bacteria. Then they used a blender to separate the virus components (DNA and proteins) from the virus shell. When only the proteins were labeled with 35S, there was no transfer of genetic material.

Historic

Aim

investigate the nature of genetic complementarity in RNA viruses, specifically tobacco mosaic virus (TMV).

Results

Free TMV RNA and protein were able to come together and form functional viruses, even when the nucleotide sequence of the free RNA was different from the original TMV RNA.

Conclusion

The results indicated that genetic complementarity did not depend on the exact sequence of nucleotides, but rather on the interaction between RNA and protein molecules. Francis Crick 1958

Aim

The experiment is related to the proposal of the "central dogma" of molecular biology.

Experiment

The hypothesis was that genetic information was unidirectional and that RNA acted as an intermediary molecule in transferring information from DNA to protein.

Results

Later, with the discovery that retroviruses could use the enzyme reverse transcriptase to synthesize DNA from RNA, the central dogma was revised to include exceptions.

Conclusion

The central dogma proposed by Crick significantly influenced the field of molecular biology, providing an early conceptual model for the transfer of genetic information.

Analytics

Heinz Fraenkel-Conrat isolated TMV RNA and separated it from the rest of the virus, leaving it as a free RNA molecule. He mixed this free RNA molecule with TMV protein to reconstruct the complete virus. Crick based his hypothesis on a variety of indirect evidence, including previous experiments on DNA replication and protein synthesis. The hypothesis was that the genetic information in RNA viruses was based on nucleotide complementarity, in the same way as base pairing in DNA. The central dogma held that genetic information flowed in a specific direction, from the DNA sequence to the synthesis of messenger RNA (mRNA) and then to the synthesis of proteins.

Historic ´

Aim

elucidate the genetic code, that is, how nucleotide sequences in DNA correspond to amino acid sequences in proteins.

Results

They analyzed the mutations and observed that the affected nucleotide sequences in the DNA corresponded to specific changes in the protein's amino acid sequence.

Conclusion

This experiment confirmed the existence of a genetic code in which sequences of nucleotide triplets in the mRNA encoded specific amino acids.

Experiment

Francis Crick e Sydney Brenner They used the nematode Caenorhabditis elegans, a model organism with convenient genetic characteristics. The hypothesis was that a specific set of nucleotide triplets (called codons) in messenger RNA (mRNA) encoded each amino acid in a protein. Crick and Brenner used chemical mutagens to induce mutations in C. elegans DNA, leading to changes in the amino acid sequences in a specific protein called collagen.

Nucleic acids deoxyribonucleic acid Definition Nucleic acids are essential macromolecules found in all living cells and in many viruses. They play a central role in the storage, transmission and expression of genetic information. There are two main types of nucleic acids: ribonucleic acid Located mainly in the cell nucleus and in small quantities in mitochondria. Molecule that carries hereditary genetic information. Structured as a double helix, consisting of two complementary chains of nucleotides. Each nucleotide includes a nitrogenous base (adenine, thymine, cytosine or guanine), a sugar (deoxyribose) and a phosphate group. catalysis of chemical reactions (ribosomal RNA or rRNA). Molecule related to DNA, usually single-stranded Contains nitrogenous bases (adenine, uracil, cytosine and guanine), a sugar (ribose) and a phosphate group It performs several cellular functions, including: translation of genetic information from DNA into protein synthesis (messenger RNA or mRNA) transport of amino acids during protein synthesis (transfer RNA or tRNA) Structure They are formed from simple subunits, called nucleotides. Each consists of a sugar- phosphate molecule with a nitrogenous side chain, or base, attached to it. There are four types of bases (adenine, guanine, cytosine and thymine or uracil)

Nucleic acids Structure: Purines are nitrogenous bases composed of double rings of carbon and nitrogen. Types: There are two purine nitrogenous bases found in nucleic acids: adenine (A) and guanine (G). nitrogenous bases Bases are nitrogen-containing ring compounds. Purine Bases Bases Pirimidinas Structure: Pyrimidines are nitrogenous bases composed of simple carbon and nitrogen rings. Types: There are three pyrimidine nitrogenous bases found in nucleic acids: cytosine (C), thymine (T) (in DNA), and uracil (U) (in RNA). There are four types of nitrogenous bases found in nucleic acids: adenine (A), thymine (T) (in DNA), uracil (U) (in RNA), cytosine (C), and guanine (G). RNA DNA NOTE: In DNA, A binds with T and its quantities are equal, just as C binds with G and its quantities are equal. A soma das bases púricas é igual a soma das bases pyramidicas

Phosphodiester bonds form the skeletal structure of the nucleic acid, while hydrogen bonds are responsible for the formation of complementary base pairs, allowing the storage and transmission of genetic information. These bonds are crucial to the function and stability of nucleic acids. Nucleic acids Connections Nucleic acids, such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), mainly contain two important bonds in their structure: Phosphodiester Bond Hydrogen Bonding This is the main bond that connects the nucleotides in the nucleic acid chain. It occurs between the phosphate group of one nucleotide and the sugar of the next nucleotide in the chain. The formation of this bond involves the loss of a water molecule (dehydration reaction) and creates a phosphate-sugar backbone in the nucleic acid molecule. The nitrogenous bases in nucleic acid (adenine, thymine, cytosine, guanine and uracil) form specific base pairs through hydrogen bonds. These hydrogen bonds are responsible for the complementarity of the bases: adenine with thymine (or uracil in RNA) and cytosine with guanine. These bonds keep the two DNA chains together in the form of a double helix.

Dogma central of Molecular Biology Genomic DNA does not control protein synthesis directly, but uses RNA as an intermediary. The flow of genetic information in cells is, therefore, from DNA to RNA and from there to protein. It is these RNA copies of DNA segments that are used directly as templates to promote protein synthesis (in a process called translation). When the cell requires a specific protein, the nucleotide sequence from the appropriate region of an extremely long DNA molecule on a chromosome is initially copied in the form of RNA (through a process called transcription). All cells, from bacteria to humans, express their genetic information in this way – a principle so fundamental that it is called central dogma of molecular biology.

To start the synthesis of a new DNA chain, a primer is needed, which are small fragments of RNA, produced and placed at the beginning of the new strand, by the enzyme primase, providing the starting point for DNA polymerase. Replicacao do ~ ~ DNA SSB proteins (Single Strand DNA Binding) bind to newly denatured DNA strands, preventing them from associating again into a double helix before replication. As the DNA strands are unwound, tension and twisting occur. Topoisomerases relieve this tension, allowing replication to proceed unimpeded. The synthesis of new DNA chains is carried out by DNA polymerase, always in the 5' to 3' direction. In bacteria, DNA polymerase III is the main replicative enzyme, while in eukaryotes, DNA polymerase delta assumes this role.

Replicacao do ~ ~ DNA DNA polymerase adds complementary DNA nucleotides to the forming DNA strand In the 3' to 5' strand this process is continuous, after the primer is inserted by primase, DNA polymerase begins to complement the leading strand. However, in the antiparallel template strand 5' to 3', the new strand, also called lagging strand or lagging strand, as DNA polymerase only makes its insertion from 5' to 3', the primer needs to be inserted at various times, and DNA polymerase inserts the nucleotides up to a certain point, until it ends. This is how several DNA fragments are formed, also known as Okazaki fragments. When strand complementarity ends, the RNA primers are removed and replaced with DNA by DNA polymerase I (in bacteria) or DNA polymerase delta (eukaryotes) Then, DNA ligase seals the gaps between the Okazaki fragments on the lagging strand, creating a single, continuous DNA strand.

We call it a

semiconservative

process, because at

the end there is an old

tape, along with a new

tape

Cell cycle